U.S. Pat. No. 5,027,092 entitled "Tripping Arrangement for Molded Case Circuit Interrupter" describes an operating mechanism that is controlled by an electronic trip unit. The trip actuator unit interfacing between the electronic trip unit and the operating mechanism is described within U.S. Pat. No. 5,172,088 entitled "Molded Case Circuit Breaker Combined Accessory Actuator Reset Lever".
The use of an electronic trip unit within such circuit breakers in place of standard thermal-magnetic trip units allows for some savings by using rating plugs to provide a single circuit breaker housing over a wide range of electrical distribution circuit ampere ratings. U.S. Pat. No. 4,728,914 and the references contained therein describe the function of the rating plug in circuit with the electronic trip unit to set the ampere rating. The use of electronic trip units has also been found to contribute to the overall cost of the circuit breaker since current transformers are required to sample the circuit current and input the current to the electronic trip unit for evaluation. It would be economically advantageous to provide a circuit breaker having the facility of electronic trip units and being economically comparable with earlier circuit breakers employing less expensive thermal-magnetic trip units.
One purpose of the invention is to provide a circuit breaker operating mechanism and contact arm assembly requiring less components than similar state-of-the-art designs resulting in a substantial savings in the cost of the components and the cost of their assembly.